[Amps] Gu78b tubes

["Thomas Hix" <w4th@hotmail.com>]

I have had several inquiries about the GU78B tube being used in the Emtron 
DX-3 amp from Australia.
A lot of the guys asking about the GU78B said they had been told, or they 
had heard, that the GU78B tube was no longer being sold, and were just about 
impossible to find.....It's news to me. I have them in stock right now, and 
I have more in the pipeline on the way to me at this time. So please....dont 
worry about being able to get the gu78b tubes in the future....my suppliers 
assure me the GU78B are in good supply.
73
Tom Hix.....Tom's Tubes......W4TH





Tom's Tubes: Specializing in Amateur Radio Amplifier Tubes, Sockets, & G3SEK 
Triode/Tetrode Boards and Kits.   http://www.tomstubes.com
> From: amps-request@contesting.com >Reply-To: amps@contesting.com >To: 
> amps@contesting.com >Subject: Amps Digest, Vol 14, Issue 8 >Date: Fri, 6 
> Feb 2004 12:00:36 -0500 (EST) > >Send Amps mailing list submissions to > 
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> so it is more specific >than "Re: Contents of Amps digest..." > > >Today's 
> Topics: > > 1. Re: Re: matching network (R.Measures) > 2. Re: Re: matching 
> network > 3. FL2100b on SIX? Possible (Etienne Swart) > 4. Re: Re: matching 
> network (R.Measures) > 5. Tube Physical Sizes (Mike Selfridge) > > 
> >---------------------------------------------------------------------- > 
> >Date: Thu, 5 Feb 2004 05:07:01 -0800 >From: R.Measures >To: "Ian White, 
> G3SEK" , > " AMPS" >Subject: Re: [Amps] Re: matching network >Message-ID: 
> <20040205130722.793AA319101@dayton.akorn.net> >Content-Type: text/plain; 
> charset="US-ASCII" >MIME-Version: 1.0 >Precedence: list >Message: 1 > > > > 
> >R. Measures wrote: > > > >>>you can safely operate *any* tetrode in class 
> AB1, > >>>cathode-driven. The requirement is that the control grid has the 
> correct > >>>negative bias, and the screen has the correct positive 
> voltage. These > >>>voltages are exactly as recommended by the manufacturer 
> for class AB1, > >>>grid-driven. > >>> > >>>For cathode drive, both grids 
> must be grounded to RF. But in order to > >>>apply different DC voltages, 
> at least one grid cannot be connected > >>>direct to chassis - it has to be 
> RF-grounded through a bypass capacitor. > >>>Because the recommended 
> voltages are measured relative to the cathode, > >>>all three power 
> supplies (anode, screen and control-grid bias) generally > >>>have to 
> 'float' relative to the chassis potential. > >>> > >>>The correct DC bias 
> voltages ensure that all the DC "grid" current goes > >>>to the screen, and 
> *none* to the control grid... in other words, correct > >>>class-AB1 
> operation. > >> > >>** Ian -- Is the power gain with cathode-driven and no 
> g1 current the > >>same as with 'super-cathode' drive -- i.e., c. 5? > > > 
> >No. > > > >In 'Single Sideband Principles & Circuits' by Pappenfus, 
> Bruene and > >Schoenike (aka the Collins company) they first describe GG 
> triode > >operation, and quote typical power gains of 7 to 20. > > > >They 
> then continue: "Tetrode tubes can also be used in cathode-driven > 
> >operation. The power gain is considerably higher, and is in the 20-to-50 
> > >region." > >** Ian -- I too once thought this was the case, but a 
> friend proved it >is not by experimenting with a 4-1000A tetrode amplifier. 
> The reason the >power gain is not: "considerably higher, and is in the 
> 20-to-50 >region." >is simply that when the grids are RF-grounded, and the 
> cathode is driven, >the driver must be able to supply the relatively large 
> cathode current on >the negative half of the driving cycle. However, when 
> the grid of a >tetrode is driven, the current is less because the only 
> current flowing >is in the grid terminator. >- For example, the grid-driven 
> tetrode amplifier I am currently >collecting parts for: The driving current 
> needed to supply the grid >terminator-R is (160w/50-ohms) ^0.5 = 1.8A. 
> However, if the cathode of >this tube were driven instead, the driver would 
> need to supply c. 5 A to >the cathode. Since P = I^2 x R, the difference in 
> driving power needed >is nothing to sneeze at. >- Humans make mistakes. I 
> make mistakes and even some blunders. Had >Pappenfus, Bruene and Schoenike 
> tried driving a tetrode via the cathode - >like my friend did, they would 
> have no doubt discovered that when a >tetrode is not grid-driven, it acts 
> like a g-g triode. The reason is >that g1/g2 amplification does not occur 
> unless driving potential exists >between the grid and the screen, with the 
> screen and cathode at the same >RF potential -- i.e., screen-cathode 
> RF-grounded. > > > >They then consider semi-cathode-driven, 
> super-cathode-driven and the RF > >feedback arrangement used on the 30S-1. 
> > > > >It's well worth reading. > >** I have a schematic diagram. The 
> power gain of a stock 30S-1 is >reportedly c. 9.5. In AB1 grid-driven 
> configuration, instead of >cathode-driven configuration, the power gain of 
> its 4cx1000A could be 50x. > > > >>- If g1 is never to be driven more 
> positive than the cathode potential, > >>why not connect it to the cathode? 
> > > > >It's all in that book. > > >** Indeed. > >cheers 
> >------------------------------ > >Date: Thu, 5 Feb 2004 10:40:58 EST 
> >From: TexasRF@aol.com >To: r@somis.org, g3sek@ifwtech.co.uk, 
> amps@contesting.com >Subject: Re: [Amps] Re: matching network >Message-ID: 
> <8b.2a214b7.2d53be0a@aol.com> >Content-Type: text/plain; charset="US-ASCII" 
> >MIME-Version: 1.0 >Content-Transfer-Encoding: 7bit >Precedence: list 
> >Message: 2 > >I have heard the term "super cathode drive" many times but 
> have not seen an >explanation of what it means. A Google search turns up 
> links that mention super >cathode drive and G2DAF circuits but no real 
> definition. > >Can anyone out there clarify this subject? > >Tnx/73, >K5GW 
> >------------------------------ > >Date: Thu, 5 Feb 2004 19:14:24 +0200 
> >From: "Etienne Swart" >To: >Subject: [Amps] FL2100b on SIX? Possible 
> >Message-ID: <006001c3ec0b$91f2a6e0$3db317c4@etienneswart> >Content-Type: 
> text/plain; > charset="iso-8859-1" >MIME-Version: 1.0 
> >Content-Transfer-Encoding: quoted-printable >Precedence: list >Message: 3 
> > >Look all over the net! >can't find a mod to put the FL2100b onto 
> >sixmeters. >Any ideas? >Thanks Etienne ZS6YFrom G3SEK@ifwtech.co.uk Thu 
> Feb 5 13:55:06 2004 >Return-Path: >X-Original-To: amps@contesting.com 
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> Feb 2004 16:48:09 +0000 >To: amps@contesting.com >From: "Ian White, G3SEK" 
> >Subject: Re: [Amps] Re: matching network >References: 
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> Fri, 06 Feb 2004 11:12:27 -0500 >X-BeenThere: amps@contesting.com 
> >X-Mailman-Version: 2.1 >Precedence: list >Reply-To: "Ian White, G3SEK" 
> >List-Id: Amps Reflector >List-Unsubscribe: , > >List-Archive: >List-Post: 
> >List-Help: >List-Subscribe: , > > > wrote: > >I have heard the term 
> "super cathode drive" many times but have not seen an > >explanation of 
> what it means. A Google search turns up links that mention > >super cathode 
> drive and G2DAF circuits but no real definition. > >  > >Can anyone out 
> there clarify this subject? > >  >Only in one respect - super cathode drive 
> and the G2DAF configuration >are totally UNconnected. > >-- >73 from Ian 
> G3SEK 'In Practice' columnist for RadCom (RSGB) > Editor, 'The VHF/UHF DX 
> Book' >http://www.ifwtech.co.uk/g3sek >------------------------------ > 
> >Date: Thu, 5 Feb 2004 12:40:45 -0800 >From: R.Measures >To: , , > " AMPS" 
> >Subject: Re: [Amps] Re: matching network >Message-ID: 
> <20040205204104.5961331940E@dayton.akorn.net> >Content-Type: text/plain; 
> charset="US-ASCII" >MIME-Version: 1.0 >Precedence: list >Message: 4 > >** 
> Super-cathode drive means g1 is tied to the cathode, the screen/g2/ >is at 
> RF-ground, and the cathode is driven. Typical power gain is >roughly = to 
> the g1-g2 amplification factor -- i.e., which is typically 4 >to 5.. . A 
> tuned input is needed to compensate for the wild swing in >input Z during 
> the drive cycle. >-- > > >I have heard the term "super cathode drive" many 
> times but have not seen an > >explanation of what it means. A Google search 
> turns up links that mention > >super > >cathode drive and G2DAF circuits 
> but no real definition. > > > >Can anyone out there clarify this subject? > 
> > > >Tnx/73, > >K5GW > > >------------------------------ > >Date: Thu, 05 
> Feb 2004 19:21:24 -0800 >From: Mike Selfridge >To: amps@contesting.com 
> >Subject: [Amps] Tube Physical Sizes >Message-ID: 
> <6.0.0.22.2.20040205190643.02d9abf0@encoreengineering.com> >Content-Type: 
> text/plain; charset="us-ascii"; format=flowed >MIME-Version: 1.0 
> >Precedence: list >Message: 5 > >A friend asked me if there was a place on 
> the web that had tube >dimensions. Electrical characteristics are 
> relatively easy to find, but >not physical sizes. I thought I'd help him 
> out, and ask the question >here. He was specifically interested in the 
> following tubes: > >3-1000Z >3CX1200A >3CX1500 > >Does anyone have one of 
> these they could measure, if not a web address for >this information? > 
> >Thanks. > >73 > >--Mike (N6QG) > >------------------------------ > 
> >_______________________________________________ >Amps mailing list 
> >Amps@contesting.com >http://lists.contesting.com/mailman/listinfo/amps > 
> > >End of Amps Digest, Vol 14, Issue 8 
> >***********************************

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